The present invention relates to a process for preparing a piecing operation in an air jet spinning arrangement, which comprises a drafting device, whose main drafting zone is bordered on its entry side by an apron roller pair connected to a first drive and on its exit side by a delivery roller pair connected to a second drive, whereby when the spinning process is interrupted the delivery of a closed staple fibre strand is stopped in the main drafting zone and a new starting end of the staple fibre strand, which is to be pieced with a thread already spun, is created, in that the apron roller pair is shut down while the delivery roller pair continues to run.
A process of this type is described in U.S. Pat. No. 5,809,764. This publication discloses, amongst others, a variation in which the apron roller pair is immediately shut down subsequent to an end break while the delivery roller pair continues to run, so that a staple fibre strand can no longer be fed to the delivery roller pair. The delivery of a closed staple fibre strand in the main drafting zone is thus inevitably stopped. As the point of separation of the staple fibre strand is deemed as unsuitable for a piecing operation according to the known publication, it is provided additionally for the preparation of a piecing operation that after the apron roller pair is stopped, but while the delivery roller pair is still running, a new starting end of the staple fibre strand is created. This occurs in that the apron roller pair starts up briefly and is then stopped again. Thus a break point is again created in the main drafting zone in the staple fibre strand, which is now considered suitable for the piecing operation. Only subsequent thereto does the actual piecing operation begin with the starting-up of the apron rollers and the rollers of the drafting device arranged upstream thereto. It is evident that because of the starting-up again of the apron roller pair and its being stopped again, that the cycle length of the piecing operation is extended. Attention is also drawn to the fact that a delicate handling of the staple fibre strand is not possible, as the delivery roller pair, as mentioned above, runs continuously at operating speed while the drive of the apron roller pair can only be switched on or off.
It is an object of the present invention to optimize the process of the above mentioned type with regard to the cycle time and the quality of the new starting end of the staple fibre strand as preparation for a piecing operation in an air jet spinning arrangement.
This object has been achieved in accordance with the present invention such that during an interruption in the spinning process, the apron roller pair and the delivery roller pair are controlled separately and are stopped one after the other in such a way that, in the main drafting zone a new starting end of the staple fibre strand is on hand and is suitable for piecing.
In the process according to the present invention, a new starting end of the staple fibre strand suitable for piecing is already created at the first stopping of the apron roller pair. A repeated starting-up and stopping of the apron roller pair is not necessary, thus reducing the length of the cycle. Because both the apron roller pair and the delivery roller pair are stopped in a controlled way, although at different times, a better quality separation point of the staple fibre strand, that is, the new starting end of the staple fibre strand, can be directly created. Both the apron roller pair and the delivery roller pair are ultimately stopped, namely in such a way that a required amount of fibres necessary for the spinning process are held nipped by the apron roller pair. As the delivery roller pair also comes to a standstill, it can be opened, which facilitates the preparation work for the piecing operation. It is a prerequisite of the present invention that individually controlled drives are provided separately for both the apron roller pair and the delivery roller pair.
In an embodiment of the present invention, it is provided that the new starting end of the staple fibre strand suitable for piecing is pulled very slightly backwards in the opposite direction to its operational rotational direction in which the apron roller pair is temporarily driven. After the separation point suitable for piecing is created, the starting end of the staple fibre strand is withdrawn to such a degree that it is just barely visible. The starting end of the staple fibre strand suitable for piecing is protected, for example against airstreams, which are necessary in practice for the feeding back of a thread end to which the staple fibre strand is to be pieced. The subsequent starting-up also takes place in a controlled way. Only after a defined starting-up time are the normal drafting speeds, that is the constant operational speeds for the apron roller pair and the delivery roller pair achieved.
In an embodiment of the present invention it is further provided that the delivery roller pair is opened shortly before it finally comes to standstill. This prevents the starting end of the staple fibre strand suitable for a piecing operation from being adversely effected, as long as the delivery roller pair is still running. Damage would occur if the delivery roller, while running down, were to turn backwards by several angular minutes directly before it came to a complete standstill, which is often the case when the drive uses a drive belt which is under tension, and this tension lessens when the drive force is discontinued. Before this can occur, the delivery roller pair is opened in order to protect the separation point of the staple fibre strand, the delivery roller pair only then being brought to a standstill.
Because of the process according to the present invention, a better quality new starting end of the staple fibre strand is generated, which quality remains after the apron roller pair and the delivery roller pair are shut down.